Oligodendrocytes that survive acute coronavirus infection induce prolonged inflammatory responses in the CNS.

Neurotropic strains of mouse hepatitis virus (MHV), a coronavirus, cause acute and chronic demyelinating encephalomyelitis with similarities to the human disease multiple sclerosis. Here, using a lineage-tracking system, we show that some cells, primarily oligodendrocytes (OLs) and oligodendrocyte precursor cells (OPCs), survive the acute MHV infection, are associated with regions of demyelination, and persist in the central nervous system (CNS) for at least 150 d. These surviving OLs express major histocompatibility complex (MHC) class I and other genes associated with an inflammatory response. Notably, the extent of inflammatory cell infiltration was variable, dependent on anatomic location within the CNS, and without obvious correlation with numbers of surviving cells. We detected more demyelination in regions with larger numbers of T cells and microglia/macrophages compared to those with fewer infiltrating cells. Conversely, in regions with less inflammation, these previously infected OLs more rapidly extended processes, consistent with normal myelinating function. Together, these results show that OLs are inducers as well as targets of the host immune response and demonstrate how a CNS infection, even after resolution, can induce prolonged inflammatory changes with CNS region-dependent impairment in remyelination

N7-Methylation of the Coronavirus RNA Cap Is Required for Maximal Virulence by Preventing Innate Immune Recognition

The ongoing coronavirus (CoV) disease 2019 (COVID-19) pandemic caused by infection with severe acute respiratory syndrome CoV 2 (SARS-CoV-2) is associated with substantial morbidity and mortality. Understanding the immunological and pathological processes of coronavirus diseases is crucial for the rational design of effective vaccines and therapies for COVID-19. Previous studies showed that 2′-O-methylation of the viral RNA cap structure is required to prevent the recognition of viral RNAs by intracellular innate sensors. Here, we demonstrate that the guanine N7-methylation of the 5′ cap mediated by coronavirus nonstructural protein 14 (nsp14) contributes to viral evasion of the type I interferon (IFN-I)-mediated immune response and pathogenesis in mice. A Y414A substitution in nsp14 of the coronavirus mouse hepatitis virus (MHV) significantly decreased N7-methyltransferase activity and reduced guanine N7-methylation of the 5′ cap in vitro. Infection of myeloid cells with recombinant MHV harboring the nsp14-Y414A mutation (rMHVnsp14-Y414A) resulted in upregulated expression of IFN-I and ISG15 mainly via MDA5 signaling and in reduced viral replication compared to that of wild-type rMHV. rMHVnsp14-Y414A replicated to lower titers in livers and brains and exhibited an attenuated phenotype in mice. This attenuated phenotype was IFN-I dependent because the virulence of the rMHVnsp14-Y414A mutant was restored in Ifnar−/− mice. We further found that the comparable mutation (Y420A) in SARS-CoV-2 nsp14 (rSARS-CoV-2nsp14-Y420A) also significantly decreased N7-methyltransferase activity in vitro, and the mutant virus was attenuated in K18-human ACE2 transgenic mice. Moreover, infection with rSARS-CoV-2nsp14-Y420A conferred complete protection against subsequent and otherwise lethal SARS-CoV-2 infection in mice, indicating the vaccine potential of this mutant. IMPORTANCE Coronaviruses (CoVs), including SARS-CoV-2, the cause of COVID-19, use several strategies to evade the host innate immune responses. While the cap structure of RNA, including CoV RNA, is important for translation, previous studies indicate that the cap also contributes to viral evasion from the host immune response. In this study, we demonstrate that the N7-methylated cap structure of CoV RNA is pivotal for virus immunoevasion. Using recombinant MHV and SARS-CoV-2 encoding an inactive N7-methyltransferase, we demonstrate that these mutant viruses are highly attenuated in vivo and that attenuation is apparent at very early times after infection. Virulence is restored in mice lacking interferon signaling. Further, we show that infection with virus defective in N7-methylation protects mice from lethal SARS-CoV-2, suggesting that the N7-methylase might be a useful target in drug and vaccine development

Eicosanoid signalling blockade protects middle-aged mice from severe COVID-19

Coronavirus disease 2019 (COVID-19) is especially severe in aged populations1. Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are highly effective, but vaccine efficacy is partly compromised by the emergence of SARS-CoV-2 variants with enhanced transmissibility2. The emergence of these variants emphasizes the need for further development of anti-SARS-CoV-2 therapies, especially for aged populations. Here we describe the isolation of highly virulent mouse-adapted viruses and use them to test a new therapeutic drug in infected aged animals. Many of the alterations observed in SARS-CoV-2 during mouse adaptation (positions 417, 484, 493, 498 and 501 of the spike protein) also arise in humans in variants of concern2. Their appearance during mouse adaptation indicates that immune pressure is not required for selection. For murine SARS, for which severity is also age dependent, elevated levels of an eicosanoid (prostaglandin D2 (PGD2)) and a phospholipase (phospholipase A2 group 2D (PLA2G2D)) contributed to poor outcomes in aged mice3,4. mRNA expression of PLA2G2D and prostaglandin D2 receptor (PTGDR), and production of PGD2 also increase with ageing and after SARS-CoV-2 infection in dendritic cells derived from human peripheral blood mononuclear cells. Using our mouse-adapted SARS-CoV-2, we show that middle-aged mice lacking expression of PTGDR or PLA2G2D are protected from severe disease. Furthermore, treatment with a PTGDR antagonist, asapiprant, protected aged mice from lethal infection. PTGDR antagonism is one of the first interventions in SARS-CoV-2-infected animals that specifically protects aged animals, suggesting that the PLA2G2D–PGD2/PTGDR pathway is a useful target for therapeutic interventions.This work is supported in part by grants from the National Institutes of Health USA (NIH; P01 AI060699 (S.P. and P.B.M.) and R01 AI129269 (S.P.)) and BIOAGE Labs (S.P.). The Pathology Core is partially supported by the Center for Gene Therapy for Cystic Fibrosis (NIH grant P30 DK-54759) and the Cystic Fibrosis Foundation. P.B.M. is supported by the Roy J. Carver Charitable Trust. L.-Y.R.W. is supported by Mechanism of Parasitism Training Grant (T32 AI007511). We thank M. Gelb (University of Washington) for Pla2g2d−/− mice.Peer reviewe

Modeling and Dynamical Analysis of Virus-Triggered Innate Immune Signaling Pathways

<div><p>The investigation of the dynamics and regulation of virus-triggered innate immune signaling pathways at a system level will enable comprehensive analysis of the complex interactions that maintain the delicate balance between resistance to infection and viral disease. In this study, we developed a delayed mathematical model to describe the virus-induced interferon (IFN) signaling process by considering several key players in the innate immune response. Using dynamic analysis and numerical simulation, we evaluated the following predictions regarding the antiviral responses: (1) When the replication ratio of virus is less than 1, the infectious virus will be eliminated by the immune system’s defenses regardless of how the time delays are changed. (2) The IFN positive feedback regulation enhances the stability of the innate immune response and causes the immune system to present the bistability phenomenon. (3) The appropriate duration of viral replication and IFN feedback processes stabilizes the innate immune response. The predictions from the model were confirmed by monitoring the virus titer and IFN expression in infected cells. The results suggest that the balance between viral replication and IFN-induced feedback regulation coordinates the dynamical behavior of virus-triggered signaling and antiviral responses. This work will help clarify the mechanisms of the virus-induced innate immune response at a system level and provide instruction for further biological experiments.</p> </div

The stability conditions at the steady states for Hill coefficients <i>n</i>₁ = <i>n</i>₂ = 1.

<p>Remark: </p

The influence of time delays on the stability of the system.

<p>The settings of the dimensionless parameters are <i>n</i>₁ = <i>n</i>₂ = 2, <i>σ</i>₁ = 0.5, <i>α</i>₂ = 5, <i>α</i>₄ = 4, <i>K</i> = 2, and the initial value is [10 5 2] for all. <i>σ</i>₂ = 1 for A and B. <i>σ</i>₂ = 5 for C and D. <i>τ</i>₁ = 5, <i>τ</i>₂ = 3, <i>τ</i>₃ = 2, <i>τ</i>₄ = 4, <i>τ</i>₅ = 6 for A and C, and <i>τ</i>₁ = 50, <i>τ</i>₂ = 30, <i>τ</i>₃ = 20, <i>τ</i>₄ = 40, <i>τ</i>₅ = 60 for B and D.</p

Stabilization of oscillation when Hill coefficients n₁ and n₂ are greater than one.

<p>(A). No delays, oscillation system. (B). <i>τ</i>₁ = 1, steady state. (C). <i>τ</i>₄ = 5, steady state. Other dimensionless parameters: <i>n</i>₁ = 4, <i>n</i>₂ = 3, <i>σ</i>₁ = 4, <i>σ</i>₂ = 0.3, <i>α</i>₂ = 2, <i>α</i>₄ = 4 and <i>K</i> = 2. The initial values are (10, 5, 2).</p

Initial concentration values of three components for the simulation in Figure 3.

<p>Initial concentration values of three components for the simulation in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048114#pone-0048114-g003" target="_blank">Figure 3</a>.</p

Schematic diagram of stability conditions with a synergistic effect.

<p>The first quadrant in the plane <i>σ</i>_1–<i>σ</i>₃ is divided into six regions , , , , and by the lines <i>σ</i>₁ = 1, <i>σ</i>₃ = 2, and the curves and </p

Schematic diagram of stability conditions without a synergistic effect.

<p>The first quadrant in the plane <i>σ</i>₁–<i>σ</i>₃ is divided into three regions , and by the lines <i>σ</i>₁ = 1, <i>σ</i>₃ = <i>1</i>, and </p